This invention relates to a transient protection circuit for a d.c. voltage supply and to a switch mode power converter including a transient protection circuit.
There are many d.c. supply requirements where the occurrence of high voltage transients can be destructive to circuits powered therefrom. This is a particular problem in the case of semiconductor circuitry, especially when implemented by integrated circuitry. When the circuitry is fed from an alternating current supply after rectification and a large capacitor cannot be directly connected across the d.c. supply lines, the smoothing effect of such a capacitor is lost so that alternative means is required to reduce the effect of mains voltage fluctuations and transients. An example is the case of switched-mode power converters such as are used for power supplies in fluorescent lamp substitutes for incandescent light bulbs.
It is known to limit a d.c. supply voltage by means of a zener diode, a varistor, or a gas discharge element, but none of these devices can reduce the maximum clamped voltage to acceptable limits in the presence of a spurious transient.